The present invention relates to subsurface drainage systems, and more particularly, to a drainage unit for an earth retaining wall system that channels subsurface water away from behind the retaining wall to relieve hydrostatic pressure that can damage the wall.
Proper drainage is an important consideration in the design and construction of earth retaining walls. In the absence of proper drainage, the water level behind a retaining wall can rise and create substantial hydrostatic pressure, which can result in severe structural damage to the retaining wall, and even cause the wall to fail.
Recently, vertical drainage sheets, commonly known as sheet drains or drainboards, have been developed to provide proper drainage for subsurface water behind a retaining wall. These sheet drains are designed to be attached to the buried face of the retaining wall to permit ground water to flow down along the face of the retaining wall inside the sheet drain to a drainage pipe located at the foundation of the wall, which channels water around the sides of the wall. Basically, the sheet drains comprise a shaped core that allows vertical passage for the flow of water down the face of the wall, and a filter fabric or screen cover surrounding the shaped core to prevent soil and other debris from entering the core and possibly clogging the drainage system.
The sheet drains are designed to be used with a perforated drainage pipe positioned at the lower end of the sheet drain at the base of the retaining wall for conveying ground water away from the wall to relieve the hydrostatic pressure. Examples of such drainage systems can be found in U.S. Pat. Nos. 4,943,185 and 4,840,515. The drainage systems disclosed in these patents, however, are focused on the construction of the sheet drains. The patents do not address the problems associated with diverting drainage water from the sheet drain directly through a retaining wall.
Typically, in order to accomplish the task of channeling subsurface drainage water through a retaining wall, a drainage pipe is often taped or otherwise tacked in place against the exterior fabric surface of a sheet drain while the retaining wall is formed, commonly using a shotcreting process. Taping or tacking the drainage pipe to the exterior of the sheet drain, however, does not provide a sturdy connection capable of withstanding the jostling that occurs during the construction of the retaining wall. As a result, the drainage pipes often become dislodged from the sheet drains, leading to delays and problems in the construction of the retaining wall. Furthermore, taping or tacking the drainage pipe to the sheet drain does not provide a tight seal between the sheet drain exterior fabric and drainage pipe. A tight seal is required to preventing soil and other debris from entering the drainage pipe and clogging up the drainage system. An additional problem with simply taping a drainage pipe to the sheet drain exterior is that only a small water collection area is created for receiving water from the sheet drain and channeling it through the retaining wall. A standard drainage pipe is three inches in diameter, and unless the water enters this three inch area, it will simply pass through the sheet drain and collect at the retaining wall foundation.
Another type of drainage system can be found in U.S. Pat. No. 6,280,117, which discloses a universal drain fitting for channeling subsurface water flows away from a retaining wall. The drain fitting, however, is designed to attach to the outer edges of a sheet drain in order to collect water that flows into the sheet drain. This limited ability of the drain fitting to attach only to the outer edges of the sheet drain creates a substantial impediment when channeling water directly through the retaining wall, as the height of the drainage pipe passing through the wall is often required to be positioned above the foundation of the retaining wall along the face of the sheet drain. Additionally, the drain fitting also requires tape to attach the drain fitting in position on the sheet drain. As noted above, tape is insufficient for securing or sealing a drainage pipe to a sheet drain when constructing a retaining wall around the drainage pipe.
Accordingly, it is an object of the present invention to provide a drainage unit for collecting water that enters a sheet drain and channeling the water into a discharge pipe that extends through a retaining wall to relieve hydrostatic pressure.
It is another object of the present invention to provide a drainage unit that may be positioned at any location on a sheet drain to collect and channel subsurface water through the retaining wall.
It is another object of the present invention to provide a drainage unit with a strong connection to the sheet drain so that the drainage unit cannot be dislodged from its position on the sheet drain during construction of the retaining wall.
It is another object of the present invention to provide a tight seal between the drainage unit and fabric of the sheet drain to prevent soil and debris from entering the drainage unit and clogging the drainage unit.
It is another object of the present invention to provide a drainage unit that channels water in the sheet drain from an area greater than the diameter of the drainage pipe to increase drainage capacity.
It is another object of the present invention to provide a drainage unit in fluid communication with the shaped core of a sheet drain to increase the ability to collect subsurface fluid flows from the sheet drain.
The above objectives are accomplished according to the present invention by providing a drainage unit for an earth retaining wall system to provide water drainage from a vertical drainage sheet through the retaining wall to reduce hydrostatic pressure on the retaining wall. The drainage unit comprises a drainage collector for attaching to a sheet drain to collect and discharge water that flows into the sheet drain. A drain hub is included in the drainage collector for being mounted in fluid communication with the sheet drain to receive water from the sheet drain and channel the water for discharge. A discharge extension is included in the drainage collector that extends from the drain hub for discharging water from the sheet drain flowing through the drain hub. The discharge extension is in fluid communication with the drain hub for discharging the water through the retaining wall. A retainer having a discharge opening is provided for engaging the discharge extension after passing through the sheet drain. The retainer secures the drain hub and discharge extension in position on the sheet drain to prevent them from being dislodged during construction of the retaining wall.
The drainage collector includes a front sealing ring for engaging a front exterior side of the sheet drain to restrict soil and other debris from entering the drainage collector. Advantageously, the retainer includes a rear sealing ring for engaging a rear exterior side of the sheet drain to restrict soil and debris from entering the drainage collector. In this construction and arrangement, soil, rocks, silt, and other matter cannot enter the drainage unit to clog the passage of water from the sheet drain to the discharge extension.
In the preferred embodiment, the front sealing ring and the rear sealing ring have a diameter greater than the drain hub to create a fluid collection chamber on the front and rear exterior sides of the sheet drain surrounding the drain hub so that an increased area of water collection is provided for channeling water into the drain hub for discharge through the retaining wall.
A plurality of fluid channels are included in the drain hub for channeling water collected from the sheet drain and the fluid collection chambers into the drain hub. Preferably, the fluid channels-comprise an extended slot formed in the drain hub that creates an opening in the drain hub having a slot length greater than a thickness of the sheet drain so that water located within the fluid collection chambers around the outside of the sheet drain is channeled through said extended slots into the drain hub.
Accordingly, a drainage unit is provided that is firmly attached to a sheet drain to prevent separation of the drainage unit from the sheet drain during construction of the retaining wall, and which relieves hydrostatic pressure by channeling water from behind the retaining wall through the retaining wall.